Plain clothes are always incredibly obvious and oblivious to that fact. I've known them to stop and search people because they are baffled someone spotted them.
while funny, I would absolutely not recommend doing this. warn the people around you, point the officer out to organizers, but do NOT interact with the police. do not give them a reason to harass or arrest you, because I promise they will take the opportunity and could possibly ruin your life.
IME they try too hard to look like street people, but it doesn't work because their clothes are clean and they bathed, your average skel substance abuser hasn’t seen a shower in 24+hrs even if they got new donated clothes.